The present invention relates to a color filter for use in a liquid crystal display panel or the like, and a method of making the same.
Methods of making a color filter for a liquid crystal display panel or the like include dyeing, pigment dispersion, printing, and electrodeposition methods. Of these fabrication methods, the printing method has a drawback with respect to accuracy, and the electrodeposition method has a drawback concerning patterning restrictions, and for those reasons the dyeing method and pigment dispersion method have been most widely used in the art.
However, the dyeing method and the pigment dispersion method each require a lithography step for forming the pixel regions for each of the first color, second color, and third color, which is a big obstacle to improving the efficiency of mass producing the color filter. One method for forming pixels without such a lithography step for each color is an inkjet method of making a color filter, which is disclosed in a number of publications, such as Japanese Patent Application Laid-Open No. 59-75205 and Japanese Patent Application Laid-Open No. 61-245106. Using an inkjet method to form the color pattern improves the efficiency of use of materials and shortens the process, and it is also possible to control the formation of the color pattern and thus obtain a color filter that is inexpensive but of a high quality.
In such a method of making a color filter using an inkjet method, one means that has been proposed to prevent ink from spreading outside of each colored region, and thus implement highly precise coloring, is to use pixel delimiting regions that are formed previously by photolithography on the substrate. Ink filling concavities are thus formed on the substrate by the pixel delimiting regions, to control the shape of a color pattern that is formed by filling these ink filling concavities with ink.
These pixel delimiting regions are often formed of an opaque material so that they also function as a black matrix (hereinafter abbreviated to BM).
In this case, a high level of precision is required for the formation of the pixel delimiting regions, but it is difficult to perform such highly precise processing while improving the mass-productivity of the process. In addition, flatness is required when forming a transparent electrode on the color filter, but it has been difficult to increase the precision of this flatness in the past.
The present invention has been devised in order to solve the above problems, and has the objective of providing a method of making an inexpensive, highly precise color filter with a reduced number of steps, as well as a color filter fabricated by that method.
A method of making a color filter in accordance with the present invention comprises: a first step of fabricating a template having a plurality of protrusions in a predetermined array;
a second step of transfer-forming an ink filling layer having a plurality of ink filling concavities by causing an ink filling layer precursor to adhere to the template, solidifying the ink filling layer precursor to form the ink filling layer, then separating the ink filling layer from the template; and
a third step of filling the ink filling cavities with inks of previously determined colors, to form a color pattern layer.
In other words, the present invention uses a template as a mold to transfer-form an ink filling layer having ink filling concavities. Once this template has been fabricated, it can be used a number of times limited by the durability thereof. Therefore step can be omitted from the process of forming the second and subsequent color filters, thus reducing the number of steps and the cost.
Specific methods of fabricating the template are described below.
(1) A step of forming a resist layer of a predetermined pattern on a substrate, then forming the protrusions on the substrate by etching to obtain the template.
This step makes it possible to control the shape and surface roughness of the protrusions in a highly precise and also unrestricted manner, by varying the etching conditions.
A silicon wafer is preferably used as this substrate. The technique of etching a silicon wafer is used as a technique in the fabrication of semiconductor devices, and enables highly precise processing.
(2) A step of forming a resist layer of a predetermined pattern on a base plate, then making the base plate and the resist layer conductive, and further using electrodeposition to deposit metal by an electroplating method to form a metal layer, and finally separating the metal layer from the base plate and the resist layer to obtain the template.
A metal template obtained by this step generally has superlative durability and separability.
This ink filling layer precursor is preferably a material which can be hardened by the application of energy. The use of such a material makes it possible for the material that forms the ink filling layer to easily fill as far as the most detailed parts of the concavities in the template, so that the shape of the protrusions on the template can be transferred accurately to form the ink filling concavities.
The energy is preferably at least one of light and heat. This makes it possible to use a general-purpose exposure apparatus, baking oven, or hotplate, enabling reductions in equipment costs and installation space.
A resin which is hardened by ultraviolet rays is an example of such a material. An acrylic resin has superlative transparency as a resin which is hardened by ultraviolet rays, and it is suitable because various commercially available resins and photosensitive materials can be used therefor.
Next, the ink is preferably injected by an inkjet method in the third step. The use of an inkjet method enables rapid application of the ink and there is also no waste of such ink.
In a further aspect of the present invention, an opaque material may be injected into concavities between the protrusions of the template after the first step but before the second step, to form an opaque layer; and
the opaque layer is integrated with the ink filling layer in the second step, by using the template on which is formed the opaque layer.
This opaque material may also be injected by an inkjet method.
The inner side surfaces of the concavities of the template may be formed in a tapered shape in such a manner that the surface area of aperture portions thereof are larger than base surfaces thereof.
These concavities of the template may also be formed in a tapered shape at aperture edge portions of inner side surfaces thereof.
If the concavities are formed in a tapered shape in this manner, the inks can be guided reliably into the concavities, thus making the color filter particularly suitable for use in a high-resolution liquid crystal panel. In addition, this configuration reduces any difference in thickness of the color pattern layer, thus reducing unevenness in color caused by factors such as differences in color tone or brightness, and thus making it possible to fabricate a color filter that provides a bright image.
Another method of making a color filter in accordance with the present invention comprises: a first step of forming a plurality of colored layers;
a second step of placing a precursor of a protective film on the colored layers; and
a third step of forming a protective film precursor layer by flattening a surface of the protective film precursor with a template having a flat surface corresponding to at least an optically transparent region (filter element) of the colored layers, then hardening the protective film precursor layer to form a protective film. This method makes it possible to form the surface of the protective film to be flat.
With the present invention, at least one concavity could be provided in a surface of the template corresponding to a region other than an optically transparent region of the colored layers;
the shape of the concavities of the template is transferred to the protective film precursor layer in the third step, to form protrusions in the protective film corresponding to the concavities; and
the protrusions act as support members (spacer) for maintaining a constant spacing (cell gap) for injecting liquid crystal into a liquid crystal panel (liquid crystal cell). This method makes it possible to form support members simultaneously with the protective film, and also easily adjust the positions at which the support members are disposed.
In this aspect of the invention, the second step could cause the concavities of the template to be positioned above and between the colored layers.
This forms support members between the colored layers. In addition, if an opaque layer (black matrix) is formed between the colored layers, protrusions that act as support members could be positioned on top of this opaque layer. For example, the opaque layer could be formed as a lattice, with the support members formed at intersection points of this lattice. Since this method makes it possible to not form support members on the colored layers, it enables an improvement in yield and also simplifies the fabrication process.
The concavities could also be formed in a circular cylindrical shape. This causes the protrusions that act as support members to have a circular cylindrical shape, making it possible to suppress disturbances in the orientation of the liquid crystal and increase the contrast of the liquid crystal panel display.
It is preferable that the protective film precursor is a material which can be hardened by the application of energy. This energy may be at least one of light and heat, for example. The protective film precursor could be a resin which is hardened by ultraviolet rays.
With this aspect of the invention, a transparent electrode film could be previously formed on the template; and
after the transparent electrode film is placed in contact with the protective film precursor, the protective film precursor layer is formed by the template, and the protective film precursor is hardened to form a protective film in the third step, the template is separated from the protective film precursor layer, leaving the transparent electrode remaining on the protective film precursor layer. This makes it possible to form the transparent electrode film in a simple manner.
A separation layer could also be formed between the template and the transparent electrode film, to promote the separation of the two components. This facilitates the removal of the template from the protective film precursor, leaving the transparent electrode film.
A color filter in accordance with the present invention comprises an ink filling layer having a plurality of ink filling concavities; and a color pattern layer formed in the ink filling cavities; and
wherein the ink filling layer is formed by causing a template having a plurality of protrusions in a predetermined array to adhere to an ink filling layer precursor, then solidifying the ink filling layer precursor.
Another color filter in accordance with the present invention comprises a plurality of colored layers; and a protective film formed on the colored layers; and
wherein the protective film is formed by flattening a surface of the protective film precursor with a template having a flat surface corresponding to at least an optically transparent region of the colored layers, then hardening the protective film precursor layer.